1. Field of the Invention
This invention relates to corrosion inhibitors for use in acidic cleaning and pickling compositions. More particularly, the invention relates to corrosion inhibitors for incorporation into acidic pickling solutions that are used to clean the surfaces of metals used in water wells and other units holding or delivering or otherwise coming into contact with, potable water.
2. Statement of the Related Art
Water wells containing potable water require periodic cleaning in order to remove scale from the well casings, well screens, pump bowls, etc. Typically, this scale is removed using an acid solution, generally a solution of hydrochloric acid. However, when such acid cleaning agents are used, several of the components forming the pumping mechanism are subject to attack by the acid, in particular, the well screen which is usually made of 304 stainless steel, the well casing which is usually made of mild steel, and especially the pump bowl which is usually cast iron. The hydrochloric acid is usually present in the cleaners in a concentration range of from 10 to 20% by weight, which, upon repeated use, can be quite damaging to the above parts. In order to protect these parts from the acid during the cleaning cycle, inhibitors have been added to the acid cleaning mixtures. However, these inhibitors have generally been of two types, namely, a toxic inhibitor such as diethylthiourea or a nontoxic inhibitor such as gelatin. The use of toxic inhibitors is, of course, quite undesirable, while the use of gelatin alone is also unsatisfactory due to the difficulty of dissolving the gelatin in the cold water and the fact that the gelatin may not protect the metal parts of the well properly, especially the cast iron pump bowl. There is therefore a compelling need for an inhibited acid solution for cleaning potable water wells in which the inhibitor is substantially nontoxic, effective, and readily soluble. Other facilities requiring non-toxic, acid cleaned corrosion inhibitors include water storage tanks, conduits, plumbing, boilers, and the like.
The use of proteins such as gelatin to inhibit the corrosion of metals in acid solution is well known; see for example, Desai, et al., Werkstoffe Korrosion 14, 739-42 (1963) which describes the use of gelatin to inhibit the organic acid corrosion of brass. Desai, et al., J. Inst. Chem. Calcutta 45, Part IV, 135-7 (1973) describes the use of gelatin as an inhibitor to protect aluminum alloys against acetic acid and chlorosubstituted acetic acids. Talati, et al., Vidya, 12(2), 182-192 (1969) discloses the use of gelatin to reduce the corrosion of aluminum and aluminum magnesium alloys when exposed to organic acids. Koshel, et al., Australas Corros. Eng., 18(8), 17-19 (1974) describes the use of casenium purum, dextrin, tannin, gelatin, or carboxymethyl cellulose to prevent weight loss due to corrosion of aluminum in hydrochloric acid. Talati, et al., Acta. Cienc. Indica., 2(3), 219-225 (1976) describes the use of inhibitors such as gelatin, glue, gum tragacanth, agar-agar, acacia, etc., to prevent the corrosion of aluminum alloys in chloroacetic acids.
A number of patents and publications describe the use of gelatin as an inhibitor against the corrosion attack by acids on iron or steel substrates. British Pat. No. 1,052,771 describes the use of gelatin, an arsenate, and a wetting agent with inorganic acids, such as phosphoric acid, to inhibit corrosion on iron or steel. Beloglazov, Uchenye Zapiski Permsk. Univ. 13, No. 3, 85-92 (1959) describes the use of inhibitors such as gelatin, casein, glycerol, etc., to protect steel against sulfuric acid. Machu, et al., Werkstoffe Korrosion, 13, 745-752 (1962) discloses the inhibition of acid corrosion in sulfuric acid by the addition of gelatin to protect a number of metals including iron metals. Beloglazov, Uch. Zap. Permsk. Gos. Univ., 19, No. 1, 37-41 (1961) discloses the use of agents such as gelatin and casein in acid solutions to prevent hydrogenation and a change in fatigue strength of steel. Cabrera, et al., Cuba Azucar, April, June, 13-20 (1977) describe the use of both ammoniated and untreated molasses to protect steel against corrosion during acid cleaning. Cabrera, et al., Cuba Azucar, July-September, 20-26 (1976) describes the use of distillery slops for preventing the acid corrosion of steel. The use of hydrolyzates of gelatin to protect certain metals from acid corrosion has also been described. For example, published Japanese Patent Application 74-35,244 describes the use of gelatin or its hydrolyzate to prevent the acid corrosion of copper zinc alloys. U.S. Pat. No. 3,505,184 describes the use of hydrolyzed protein as an inhibitor in a zinc electrodepositing bath. Published Czechoslovakian Patent Application 153,709 discloses the use of protein hydrolyzate to inhibit the corrosion of steel in 39% HCl. U.S. Pat. No. 4,209,418 describes the use of gelatin mixed with benzimidazole compounds (which are toxic), as providing corrosion inhibition for aqueous carboxylic acid metal cleaning solutions. Ammoniated ethylenediamine tetracetic acid (EDTA) and/or ammoniated citric acid are preferred as the carboxylic acids. Minor amounts of ethylquinolinium iodide and/or 2-thio-4,6-dimethyl pyrimidine hydrochloride may be present, although no other ingredients are disclosed. Both of these minor additives, or their analogs, are listed as toxic substances in the Chemical Abstracts Service Registry, the iodide having No. 634-35-5.